In the manufacture of next generation integrated circuits, the fabrication of gate electrodes for complementary metal-oxide-semiconductor (CMOS) transistors has advanced to replace silicon dioxide and polysilicon with high-k dielectric materials and metal. A replacement metal gate process is often used to form the gate electrode. A typical replacement metal gate process begins by forming a high-k dielectric material and a sacrificial gate between a pair of spacers on a semiconductor substrate. After further processing steps, such as an annealing process, the sacrificial gate is removed and the resulting trench is filled with one or more metal layers. The metal layers can include workfunction metals as well as electrode metal layers.
Processes such as atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD), electroplating (EP), and electroless plating (EL) may be used to deposit the one or more metal layers that form the metal gate electrode. Unfortunately, as CMOS transistor dimensions decrease, for instance, as transistor gate lengths reach 45 nm and below, issues such as trench overhang and void formation become more challenging and more rampant, especially when a dual-metal gate electrode is needed. This is because at smaller dimensions, the aspect ratio of the trench used to form the metal gate electrode becomes very aggressive as the dual-metal layers are deposited. As will be recognized by those of ordinary skill in the art, metallization of such a high aspect ratio trench quite often results in void formation.
Accordingly, an improved process of forming dual-metal gate electrodes for CMOS transistors at the 45 nm node level and beyond is needed.